Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

EASY QUESTION, RESPONse

  1. Oct 19, 2009 #1
    EASY QUESTION, URGENT RESPONse

    when u typically hit a reset buton on a breadboard, it is usually closing the circuit to ground.

    However lets say u want the reset button to power to vdd when hit and be grounded when not hit. How would u implement this?
     
  2. jcsd
  3. Oct 20, 2009 #2

    vk6kro

    User Avatar
    Science Advisor

    Re: EASY QUESTION, URGENT RESPONse

    Connect it as in the attached diagram.

    The 4.7 K resistor holds the reset pin low except if you push the switch, when the reset pin will go high.
     

    Attached Files:

  4. Oct 20, 2009 #3

    MATLABdude

    User Avatar
    Science Advisor

    Re: EASY QUESTION, URGENT RESPONse

    We usually pull low (with the resistor in vk6kro's diagram attached to the Vdd, and GND attached to the switched terminal, a.k.a. a pull-up configuration) to ensure that the pin always sees ground.

    I was burnt on this once when I used the BJT side of some optoisolators with pull-downs (and, to boot, calculated values to drive the optos near the edge of saturation). Unfortunately, the high impedance supply meant that I had a voltage divider with the pull-down resistor. This worked great when I tested with the bench supply and with some experimental switch flipping. It didn't work so great when it was exposed to the 4kHz PWM.

    Moral of the story: use your function generator and oscilloscope!
     
  5. Oct 20, 2009 #4

    vk6kro

    User Avatar
    Science Advisor

    Re: EASY QUESTION, URGENT RESPONse

    lets say u want the reset button to power to vdd when hit and be grounded when not hit. How would u implement this?

    That was the question. Why pull low when the question asks for reset to be pulled high?

    Some chips require a high on the reset pin to reset. You don't get a choice.
     
  6. Oct 20, 2009 #5

    MATLABdude

    User Avatar
    Science Advisor

    Re: EASY QUESTION, URGENT RESPONse

    True. Just thought I'd add some enrichment discussion. (If, in fact, it's deemed as such).
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook